The invention relates to a motor vehicle having a generator, electric consuming devices, a first electric energy storage device and a second energy storage device connected in parallel to the first energy storage device. The two electric energy storage devices having at least partially overlapping characteristic open-circuit voltage curves in the voltage range. The first energy storage device has a first state-of-charge-dependent characteristic charging internal-resistance curve. The second energy storage device has a second state-of-charge-dependent characteristic charging internal-resistance curve. The first energy storage device has a first state-of-charge-dependent characteristic discharging internal-resistance curve and the second energy storage device has a second state-of-charge-dependent characteristic discharging internal-resistance curve.
According to German Patent document DE 10 2009 008 177 A1, in the case of vehicles having a plurality of electric consuming devices (electrical loads), the electric energy supply is ensured by one or more batteries or by a generator. An onboard power supply system architecture having two energy storage devices is suggested, which can be connected electrically in parallel by way of a coupling element. The coupling element is adjusted as a function of the state of the ignition in order to ensure a high availability of the consuming devices in every operating condition of the vehicle and to avoid a starting-voltage drop in the onboard power supply system during engine starts, particularly in the case of an engine start-stop function.
German Patent document DE 10 2010 062 116 A1 describes a 2-energy-storage-device onboard power supply system for a vehicle having two permanently parallel-connected energy storage devices whose characteristic voltage curves partially overlap.
It is an object of the invention to provide an improved motor vehicle equipped with a generator, electric consuming devices, a first electric energy storage device and a second energy storage device connected in parallel to the first energy storage device. The two electric energy storage devices having at least partially overlapping characteristic open-circuit voltage curves in the voltage range. The first energy storage device has a first state-of-charge-dependent characteristic charging internal-resistance curve and the second energy storage device has a second state-of-charge-dependent characteristic charging internal-resistance curve. The first energy storage device has a first state-of-charge-dependent discharging internal-resistance curve and the second energy storage device has a second state-of-charge-dependent characteristic discharging internal-resistance curve.
This and other objects are achieved by a motor according to the invention, wherein the first characteristic charging internal-resistance curve extends over an entire relative state-of-charge range in the direction of higher resistances essentially above the second characteristic charging internal-resistance curve, and the first characteristic discharging internal-resistance curve extends over an entire relative state-of-charge range in the direction of higher resistances essentially below the second characteristic discharging internal-resistance curve. The two energy storage devices are interconnected with one another in a voltage-neutral manner.
The described relative positions of the characteristic charging internal-resistance curves or the characteristic discharging internal-resistance curves may have anomalies in the edge areas of the relative state-of-charge range, i.e. at or close to 0% relative state-of-charge (SoC), as well as at or close to 100% relative state-of-charge, which in these edge areas have a different course than the described essential course. The advantages and effects of the invention remain unaffected by these anomalies, so that the anomalies do not limit the invention. As an example, a considerable rise of the characteristic discharging internal-resistance curve in the case of a lead acid battery as the first energy storage device with respect to the 0% state-of-charge can be mentioned, which possibly exceeds the characteristic discharging internal-resistance curve of a lithium ion battery as the second energy storage device with respect to the 0% state-of-charge in the direction of higher resistances. The characteristic discharging internal-resistance curve of the lead acid battery essentially extends in the direction of higher resistances but below the characteristic discharging internal-resistance curve of the characteristic discharging internal-resistance curve of the lithium ion battery, to which characteristics essential to the invention are linked.
In addition, the considerations of the characteristic resistance curves relate to a temperature range which, when used in automotive engineering, is considered to be a typical temperature range for an energy storage device, i.e. from approximately −20° C. to approximately +60° C.
A voltage-neutral wiring means that, essentially, a direct galvanic connection exists between the two energy storage devices. In particular, voltage-providing or voltage-coupling components, such as a switch, a relay or a d.c. converter, are not necessarily situated between the two energy storage devices. As a result of the parallel connection of the two storage devices, these are therefore on the same electric potential at every operating point. In the following, this voltage will be called the coupling voltage.
According to a preferred embodiment of the invention, the first electric energy storage device, in the case of an approximately fully charged state, has an open-circuit voltage which corresponds essentially to a relative state-of-charge of the second energy storage device in the lower to medium range.
This means that the two energy storage devices are constructed such that the fully charged state of the first energy storage device results in a coupling voltage at which the second energy storage device is in a lower to medium state-of-charge range. The lower to medium state-of-charge range can be estimated at 5%-60% of the relative state-of-charge.
Furthermore, it is a technical advantage for the motor vehicle to include a control unit and a battery sensor, for the battery sensor to be assigned to the second energy storage device and, by the time-related integration of a charging current and of a discharging current of the second energy storage device, for the state-of-charge of the second energy storage device to be determinable by means of the battery sensor and/or of the control unit.
According to a preferred variant of the invention, by way of the control unit, a regenerative charging current of the energy storage device can be set and a consuming-device-related discharging current of the energy storage device can be set, the second electric energy storage device being operated in a time-dependent course in a specified desired state-of-charge range, and the desired state-of-charge range is in the essentially lower to medium state-of-charge range of the second energy storage device.
The second energy storage device is therefore operated in a specified state-of-charge range, which is in the range of lower to medium states of charge of the second energy storage device. This means that, during this operation, the first energy storage device is approximately fully charged.
In addition, it is very advantageous for a regenerative charging current to be settable in a recovery phase by the control unit in a motor vehicle having a braking-energy recovery function, which charging current, in a time-dependent course, results in a state-of-charge of the second energy storage device that is situated in the direction of higher states of charge above the desired state-of-charge range, and in driving phases which do not represent recovery phases, for a regenerative charging current or a consumption-related discharging current to be set by the control unit such that the charging current and the discharging current lead the state-of-charge of the second electric energy storage device in a time-dependent course into the desired state-of-charge range or maintain the state-of-charge of the second electric energy storage device in a time-dependent course in the desired state-of-charge range.
If, as an alternative or in addition to the braking energy recovery function, the motor vehicle has an automatic engine stop-start function, it is an advantageous variant of the invention for a discharge current to be settable in an engine stop phase by the control unit. The discharge current, in a time-dependent course, leads to a state-of-charge of the second energy storage device which is situated in the direction of higher states of charge below the desired state-of-charge range. In driving phases, which represent no engine-stop phase, a regenerative charging current and a consuming-device-related discharging current are set by the control unit such that the charging current and the discharging current lead the state-of-charge of the second electric energy storage device in a time-dependent course into the desired state-of-charge-range or maintain the state-of-charge of the second electric energy storage device in a time-dependent course in the desired state-of-charge range.
The invention is based on the following considerations.
The starting point is a conventional vehicle having a single lead acid battery as its energy storage device for the basic onboard power supply system, wherein the vehicle may be equipped with micro-hybrid functionalities such as a braking energy recovery function (BER) with an automatic engine stop-start system (MSA).
Operating strategies for the conventional onboard power supply system may consist of maximizing the service life of the lead acid battery (LAB). In the LAB technology known to the person skilled in the art, this can be achieved particularly in the case of a lasting full charging of the LAB, i.e. when a full charging strategy is used. However, in order to open up the possibility of the recovery of electric energy converted from kinetic energy also with the LAB, a targetedly partially discharged operation of the LAB is selected, which may have a disadvantageous effect on the service life of the LAB. This may have a particularly disadvantageous effect in unfavorable operating conditions when the state-of-charge of the LAB is additionally lowered by frequent stopping phases by the MSA and by an excessive discharging in the parking and after-running phase of the vehicle.
Modern 2-battery concepts have energy storage devices with different chemical techniques, as, for example, the combination of a lead acid battery with a lithium ion battery (LiB).
In the case of voltage-neutral parallel-connected energy storage devices, i.e. in the case of a galvanic connection, a voltage common to the energy storage devices occurs, which is called a coupling voltage.
For such an energy storage system, a skillful and simultaneously robust operating strategy is provided. This operating strategy makes it possible to utilize the specific advantages of the two energy storage devices of the energy storage device system.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.